Method and a device for generating report data related to an interface status

ABSTRACT

Disclosed is a method and a device for generating report data related to a status of an interface of a network element are presented. The method includes: activating a delay timer when the interface status changes, setting delay-based data to express the interface status at the end of a delay determined by the delay-timer, setting dampening-based data to express the interface status if a penalty value fulfils a pre-determined condition and otherwise to express that the interface is non-utilizable, and setting the report data to express that the interface is utilizable if both the delay-based data and the dampening-based data express that the interface is utilizable. The penalty value is decreased with a dampening rule, and the penalty value is increased when the interface becomes non-utilizable and increasing the penalty value within a time-window is below a desired limit.

FIELD OF THE DISCLOSURE

The disclosure relates generally to producing report data suitable forinforming a control-plane and/or another entity about a status of aninterface of a network element. More particularly, the disclosurerelates to a method and to a device for generating report data relatedto a status of an interface of a network element. Furthermore, thedisclosure relates to a computer program for generating report datarelated to a status of an interface of a network element. Furthermore,the disclosure relates to a network element such as e.g. a router.

BACKGROUND

In a data transfer network, there is often a need to communicatestatuses of interfaces of a network element to a control plane which rune.g. routing protocols. Furthermore, there can be a need to communicatethe statuses of the interfaces to other physical and/or logical entitieswhich run e.g. protection and/or other functionalities dependent on thestatuses of the interfaces. The network element can be for example anInternet Protocol “IP” router, a MultiProtocol Label Switching “MPLS”router “LSR”, a packet optical switch, an Ethernet switch, and/or asoftware-defined networking “SDN” controlled network element. Typically,it would be however disadvantageous to communicate the status of aninterface as such because the status can flap frequently between anon-state where the interface is utilizable and an off-state where theinterface is not utilizable. For example, the packet optical convergenceleads in many cases to situations where there is a packet opticalnetwork on a route between two network elements. When the packet opticalnetwork carries out e.g. re-routing, this causes that each of theabove-mentioned network elements sees that an interface connected to alink providing an access to the other network element has a temporallyisolated burst of status changes between the on-state and the off-state.For example, the control plane would be heavily loaded if it were forcedto react to all these status changes.

Thus, there is a need to generate report data for communicating thestatus of an interface to the control plane and/or to other appropriateentities so that status flapping is filtered out from the report databut it still provides sufficient information about the status of theinterface.

Carrier delay and interface flap dampening are two commonly knownmethods for generating report data that informs the control-plane and/orother appropriate entities about a status of an interface of a networkelement. The carrier delay is based on a delay timer which is activatedwhen the status of the interface changes and the delay timer isinactive. The above-mentioned report data is set to express the statusof the interface prevailing at the end of a delay determined by thedelay-timer. Thus, status flapping occurring during the delay isfiltered out from the report data. A general problem of the carrierdelay is that its delay timer may be in synchronism with repeatingon-off status changes so that it erroneously expresses the on-state evenif there are the repeating on-off status changes and thereby theinterface is not utilizable. The interface flap dampening is based onpenalty accumulation with a decay mechanism to keep the report dataindicative of the off-state when a status of an interface flapsfrequently. A problem of the interface flap dampening is that thepenalty may reach a high value during a temporally isolated burst ofon-off status changes and, after the burst, it may take a long time forthe decay mechanism to decrease the penalty so much that the report datagets indicative of the on-state. Thus, the interface flap dampening mayexpress the off-state for a too long time after the burst.Straightforward parallel and series connections of the interface flapdampening and the carrier delay do not solve the above-mentionedproblems. For example, in a case of a parallel connection with theAND-logic, the interface flap dampening reports the off-state for a toolong time after a burst of on-off status changes and thereby the resultof the AND-logic also reports the off-state for the too long time afterthe above-mentioned burst.

SUMMARY

The following presents a simplified summary in order to provide a basicunderstanding of some aspects of various invention embodiments. Thesummary is not an extensive overview of the invention. It is neitherintended to identify key or critical elements of the invention nor todelineate the scope of the invention. The following summary merelypresents some concepts in a simplified form as a prelude to a moredetailed description of exemplifying embodiments of the invention.

In accordance with the invention, there is provided a new device forgenerating report data related to a status of an interface of a networkelement, the report data being suitable for informing a control planeabout the status of the interface so that flapping between utilizableand non-utilizable states of the interface is filtered out from thereport data. A device according to the invention comprises a delay timerand a processor system configured to:

-   -   receive status data having an on-value when the interface is        utilizable and an off-value when the interface is        non-utilizable,    -   initialize, in response to a situation which the status data is        received for a first time, delay-based data to have a value of        the status data and dampening-based data to have the value of        the status data,    -   activate the delay timer in response to a situation in which the        status data changes while the delay timer is inactive,    -   set, at an end of a delay determined by the delay timer, the        delay-based data to have a value of the status data occurring at        the end of the delay,    -   set, regardless of the delay timer, the dampening-based data to        have the value of the status data if a penalty value fulfils a        condition defined with one or more penalty thresholds, and        otherwise set the dampening-based data to have the off-value,        and    -   set, regardless of the delay timer, the report data to have a        value of the delay-based data if the dampening-based data has        the on-value, and otherwise set the report data to have the        off-value.

In order to manage the above-mentioned penalty value, the processorsystem is configured to:

-   -   set, regardless of the delay timer, penalty control data to have        a preventive value in response to a situation in which        increasing the penalty value during a time window exceeds a        predetermined limit, the time-window including the current        moment of time and having a pre-determined temporal length,    -   increase, regardless of the delay timer, the penalty value in        response to a situation in which i) the status data changes from        the on-value to the off-value and ii) the penalty control data        has a value other than the preventive value, and    -   decrease, regardless of the delay timer and in response to a        situation in which the penalty value is greater than zero, the        penalty value in accordance with a predetermined rule over time.

As the penalty value is allowed to be increased only when the increasingduring the time window does not exceed the predetermined limit, theincrease rate of the penalty value is limited. This limits the increaseof the penalty value during for example a temporally isolated burst ofon-off status changes. Therefore, the above-described device can betuned by selecting appropriate values for the limit related toincreasing the penalty value, for the decrease rate of the penaltyvalue, and for the temporal length of the time-window so that the devicedoes not report the off-state for a too long time after the burst. Theincreasing the penalty value can be measured in many ways. For example,an amount added to the penalty value during a time window can be used asa quantity indicative of the increasing the penalty value. For anotherexample, the number of times the penalty value has been increased duringa time window can be used as a quantity indicative of the increasing thepenalty value.

In this document, the “increase the penalty value” means increasing theabsolute value of a difference between the penalty value and a fixedbottom value, e.g. zero, of the penalty value. Correspondingly, the“decrease the penalty value” means decreasing the absolute value of thedifference between the penalty value and the fixed bottom value. It is aquestion of interpretation whether e.g. a voltage signal having a givenpolarity or a digital signal having a given bit vector is deemed to benegative or positive. Thus, the above-presented definition for a deviceaccording to the invention covers analog implementations irrespective ofpolarity and a bottom value of an analog signal corresponding to thepenalty value as well as digital implementations irrespective of amethod for encoding the penalty value into a bit vector. For the sake ofclarity and brevity, the penalty value is handled in this document as anon-negative number whose fixed bottom value is zero irrespective of theimplementation of a device according to the invention.

In accordance with the invention, there is provided also a new networkelement that can be for example an Internet Protocol “IF” router, amultiprotocol label switching “MPLS” router “LSR”, a packet opticalswitch, an Ethernet switch, and/or a software-defined networking “SDN”controlled network element. The network element comprises:

-   -   interfaces for connecting to a data transfer network,    -   a processing system for running a control plane for configuring        the network element to operate as a part of the data transfer        network and for running a data plane for forwarding data, and    -   a device according to the invention for generating report data        so as to inform at least the control plane about a status of at        least one of the interfaces of the network element.

In accordance with the invention, there is provided also a new methodfor generating report data related to a status of an interface of anetwork element, the report data being suitable for informing a controlplane about the status of the interface so that flapping betweenutilizable and non-utilizable states of the interface is filtered outfrom the report data. A method according to the invention comprises:

-   -   receiving status data having an on-value when the interface is        utilizable and an off-value when the interface is        non-utilizable,    -   initializing, in response to a situation which the status data        is received for a first time, delay-based data to have a value        of the status data and dampening-based data to have the value of        the status data,    -   activating a delay timer in response to a situation in which the        status data changes while the delay timer is inactive,    -   setting, at an end of a delay determined by the delay timer, the        delay-based data to have a value of the status data occurring at        the end of the delay,    -   setting, regardless of the delay timer, the dampening-based data        to have the value of the status data if a penalty value fulfils        a condition defined with one or more penalty thresholds, and        otherwise setting the dampening-based data to have the        off-value, and    -   setting, regardless of the delay timer, the report data to have        a value of the delay-based data if the dampening-based data has        the on-value, and otherwise setting the report data to have the        off-value.

In order to manage the above-mentioned penalty value, the methodcomprises:

-   -   setting, regardless of the delay timer, penalty control data to        have a preventive value in response to a situation in which        increasing the penalty value during a time window exceeds a        predetermined limit, the time-window including the current        moment of time and having a pre-determined temporal length,    -   increasing, regardless of the delay timer, the penalty value in        response to a situation in which i) the status data changes from        the on-value to the off-value and ii) the penalty control data        has a value other than the preventive value, and    -   decreasing, regardless of the delay timer and in response to a        situation in which the penalty value is greater than zero, the        penalty value in accordance with a predetermined rule over time.

In accordance with the invention, there is provided also a new computerprogram for generating report data related to a status of an interfaceof a network element, the report data being suitable for informing acontrol plane about the status of the interface so that flapping betweenutilizable and non-utilizable states of the interface is filtered outfrom the report data. A computer program according to the inventioncomprises computer executable instructions for controlling aprogrammable processor to:

-   -   receive status data having an on-value when the interface is        utilizable and an off-value when the interface is        non-utilizable,    -   initialize, in response to a situation which the status data is        received for a first time, delay-based data to have a value of        the status data and dampening-based data to have the value of        the status data,    -   activate a delay timer in response to a situation in which the        status data changes while the delay timer is inactive,    -   set, at an end of a delay determined by the delay timer, the        delay-based data to have a value of the status data occurring at        the end of the delay,    -   set, regardless of the delay timer, the dampening-based data to        have the value of the status data if a penalty value fulfils a        condition defined with one or more penalty thresholds, and        otherwise set the dampening-based data to have the off-value,        and    -   set, regardless of the delay timer, the report data to have a        value of the delay-based data if the dampening-based data has        the on-value, and otherwise set the report data to have the        off-value.

In order to manage the above-mentioned penalty value, the computerprogram comprises computer executable instructions for controlling theprogrammable processor to:

-   -   set, regardless of the delay timer, penalty control data to have        a preventive value in response to a situation in which        increasing the penalty value during a time window exceeds a        predetermined limit, the time-window including the current        moment of time and having a pre-determined temporal length,    -   increase, regardless of the delay timer, the penalty value in        response to a situation in which i) the status data changes from        the on-value to the off-value and ii) the penalty control data        has a value other than the preventive value, and    -   decrease, regardless of the delay timer and in response to a        situation in which the penalty value is greater than zero, the        penalty value in accordance with a predetermined rule over time.

In accordance with the invention, there is provided also a newnon-transitory computer readable medium, e.g. a compact disc “CD”. Anon-transitory computer readable medium according to the invention isencoded with a computer program according to the invention.

Various exemplifying and non-limiting embodiments of the invention aredescribed in accompanied dependent claims.

Various exemplifying and non-limiting embodiments of the invention bothas to constructions and to methods of operation, together withadditional objects and advantages thereof, will be best understood fromthe following description of specific exemplifying and non-limitingembodiments when read in conjunction with the accompanying drawings.

The verbs “to comprise” and “to include” are used in this document asopen limitations that neither exclude nor require the existence of alsoun-recited features.

The features recited in dependent claims are mutually freely combinableunless otherwise explicitly stated. Furthermore, it is to be understoodthat the use of “a” or “an”, i.e. a singular form, throughout thisdocument does not exclude a plurality.

BRIEF DESCRIPTION OF THE FIGURES

Exemplifying and non-limiting embodiments of the invention and theiradvantages are explained in greater detail below with reference to theaccompanying drawings, in which:

FIG. 1 shows a schematic illustration of a network element according toan exemplifying and non-limiting embodiment of the invention, and

FIG. 2 shows a flowchart of a method according to an exemplifying andnon-limiting embodiment of the invention for generating report datarelated to a status of an interface of a network element.

DESCRIPTION OF EXEMPLIFYING AND NON-LIMITING EMBODIMENTS

The specific examples provided in the description below should not beconstrued as limiting the scope and/or the applicability of theaccompanied claims. Lists and groups of examples provided in thedescription below are not exhaustive unless otherwise explicitly stated.

FIG. 1 shows a schematic illustration of a network element 101 accordingto an exemplifying and non-limiting embodiment of the invention. Thenetwork element 101 can be for example an Internet Protocol “IF” router,a multiprotocol label switching “MPLS” switch, a packet optical switch,an Ethernet switch, and/or a software-defined networking “SDN”controlled network element. The network element 101 comprises interfaces109 for receiving data from a data transfer network 111 and fortransmitting data to the data transfer network 111. The network element101 comprises a processing system 102 for running control planefunctionalities for configuring the network element 101 to operatetogether with the data transfer network 111 and for running data planefunctionalities for forwarding data. The control plane runs e.g. routingprotocols which are dependent on statuses of the interfaces 109. Forexample, there can be a need for re-routing if the status of a giveninterface changes from the on-state in which the interface is operablefor data transfer to the off-state in which the interface is no moreoperable for data transfer. Furthermore, the processing system 102 canbe configured to run protection and/or other functionalities which aredependent on the statuses of the interfaces 109.

The network element 101 comprises a device 103 according to anexemplifying and non-limiting embodiment of the invention for generatingreport data R based on the statuses of the interfaces 109 and forcommunicating the report data R to the control plane and to possibleother entities which are implemented with the processing system 102 andwhich are dependent on the statuses of the interfaces 109. The device103 comprises a processor system 104 and a delay timer 110. In FIG. 1,the processor system 104 and the delay timer 110 are presented asseparate entities but in a practical implementation the delay timer canbe implemented with the processor system 104. Furthermore, it is alsopossible that the processing system 102 and the processor system 104 areimplemented with same hardware elements. In this exemplifying case, theprocessing system 102, the processor system 104, and the delay timer 110are mere logical entities.

The processor system 104 of the device 103 is configured to receive, foreach interface, status data S having an on-value when the interfaceunder consideration is utilizable and an off-value when the interface isnon-utilizable. The processor system 104 is configured to activate thedelay timer 110 in response to a situation in which the status data Schanges while the delay timer 110 is inactive. The processor system 104is configured to wait for a delay determined by the delay timer and thenset, at the end of the delay, delay-based data DE to have the value ofthe status data S occurring at the end of the delay. Thus, possibleflapping of the status data S during the delay is filtered out from thedelay-based data DE.

The processor system 104 is configured to set dampening-based data DM tohave the value of the status data S if a penalty value P fulfils acondition defined with one or more penalty thresholds, and otherwise toset the dampening-based data DM to have the off-value. Examples of thecondition defined with the one or more penalty thresholds are presentedlater in this document. The processor system 104 is configured to setthe report data R to have the value of the delay-based data DE if thedampening-based data DM has the on-value, and otherwise to set thereport data R to have the off-value.

In order to manage the above-mentioned penalty value P, the processorsystem 104 is configured to carry out the following actions: a) settingpenalty control data PC to have a preventive value if an amountexceeding an increase limit has been added to the penalty value P duringa time-window including the current moment of time and having apre-determined temporal length, b) increasing the penalty value with apenalty increment AP in response to a situation in which the status dataS changes from the on-value to the off-value and the penalty controldata PC has a value other than the preventive value, and c) decreasingthe penalty value P in accordance with a predetermined rule over time.As the amount allowed to be added to the penalty value P within thetime-window is limited, the increase rate of the penalty value P islimited. This limits the increase of the penalty value P during forexample a temporally isolated burst of on-off changes in the status dataS. The above-mentioned predetermined rule for decreasing the penaltyvalue P can be for example such that the penalty value P is multipliedthe with a coefficient α less than one at successive moments of time,i.e. P_(i+1)=αP_(i), where P_(i) is the penalty value when time=t_(i)and P_(i+1) is the penalty value when time=t_(i+1)=t_(i)+Δt, where Δt isa time increment.

In a device according to an exemplifying and non-limiting embodiment ofthe invention, the processor system 104 is configured to set the penaltycontrol data PC to have the preventive value if the penalty value P hasbeen increased a pre-determined number of times during the time-window.The pre-determined number can be for example but not necessarily 1, 2,or 3.

In a device according to an exemplifying and non-limiting embodiment ofthe invention, the processor system 104 is configured to begin a newtime-window at each time when a change of the status data S from theon-value to the off-value causes an activation of the delay timer 110.The temporal length of the time-window is advantageously the temporallength of the delay determined by the delay timer. The above-mentionedchange of the status data S can be deemed to belong to the time-windowwhich is started due to the change of the status data S. In thisexemplifying case, the processor system 104 increases the penalty valueP at the beginning of the time-window. The increase of the penalty valuecarried out at the beginning of the time-window represents at least apart of the amount being added to the penalty value during the startedtime-window.

In a device according to an exemplifying and non-limiting embodiment ofthe invention, the processor system 104 is configured to begin a newtime-window at each time when a change of the status data S from theoff-value to the on-value causes an activation of the delay timer 101.The temporal length of the time-window is advantageously the temporallength of the delay determined by the delay timer.

In a device according to an exemplifying and non-limiting embodiment ofthe invention, the processor system 104 is configured to begin a newtime-window at each time when a change of the status data S from theon-value to the off-value or from the off-value to the on-value causesan activation of the delay timer 101. The temporal length of thetime-window is advantageously the temporal length of the delaydetermined by the delay timer.

In a device according to an exemplifying and non-limiting embodiment ofthe invention, the processor system 104 is configured to set thetime-window to be a sliding time-window so that the current moment oftime is the end-point of the sliding time-window and the time-windowslides forward along time. In this exemplifying case, the processorsystem 104 is configured to check whether or not an amount added to thepenalty value P during a time interval from t-TW to t exceeds theincrease limit, where t is the current moment of time and TW is thetemporal length of the time-window.

In a device according to an exemplifying and non-limiting embodiment ofthe invention, the processor system 104 is configured to set thetime-window to be a step-wise proceeding time-window so that thetime-window is shifted step-wise forward by the temporal length TW ofthe time-window when the current moment of time reaches the end-point ofthe time-window. In this exemplifying case, the processor system 104 isconfigured to check whether or not an amount added to the penalty valueP during a time interval from t-TW_(elapsed) to t exceeds the increaselimit, where t is the current moment of time, and TW_(elapsed) is thetemporal length of the elapsed part of the current time-window.

In a device according to an exemplifying and non-limiting embodiment ofthe invention, the processor system 104 is configured to set thedampening-based data DM to have the value of the status data S if thepenalty value P is less than a penalty threshold P_(th), and otherwiseto set the dampening-based data DM to have the off-value.

In a device according to another exemplifying and non-limitingembodiment of the invention, the processor system 104 is configured toset the dampening-based data DM to have the value of the status data Sif one of the following conditions a) and b) is fulfilled, and otherwiseto set the dampening-based data to have the off-value:

-   -   a) the penalty value P is less than a lower penalty threshold        P_(thL), or    -   b) the penalty value P is at least the lower penalty threshold        P_(thL) and less than a higher penalty threshold        P_(thH)>P_(thL), and the penalty value P has not reached the        higher penalty threshold P_(thH) after a most recent time when        the penalty value P was less than the lower penalty threshold        P_(thL).

An advantage of the above-described approach based on the two penaltythresholds P_(thL) and P_(thH) is that a situation where the penaltyvalue P oscillates around one of the thresholds does make thedampening-based data DM to oscillate between the off-value and theon-value when the status data S happens to have the on-value.

The processing system 102 of the network element 101 comprises one ormore processors 105 each of which can be for example a programmableprocessor provided with appropriate software, a dedicated hardwareprocessor such as for example an application specific integrated circuit“ASIC”, or a configurable hardware processor such as for example a fieldprogrammable gate array “FPGA”. The processing system 102 may compriseone or more memory circuits 106 each of which can be e.g. arandom-access memory circuit “RAM” or a content-access memory circuit“CAM”. The processor system 104 may comprise one or more processors 107,each of which can be a programmable processor provided with appropriatesoftware, a dedicated hardware processor such as for example anapplication specific integrated circuit “ASIC”, or a configurablehardware processor such as for example a field programmable gate array“FPGA”. The processor system 104 may comprise one or more memorycircuits 108 each of which can be e.g. a random-access memory circuit“RAM”. It is also possible that the processing system 102 and theprocessor system 104 are implemented with same hardware elements.

FIG. 2 shows a flowchart of a method according to an exemplifying andnon-limiting embodiment of the invention for generating report datarelated to a status of an interface of a network element. A methodaccording to the invention comprises the following actions:

-   -   action 201: receiving status data having an on-value when the        interface is utilizable and an off-value when the interface is        non-utilizable,    -   action 202: activating a delay timer in response to a situation        in which the status data changes while the delay timer is        inactive,    -   action 203: setting, at an end of a delay determined by the        delay timer, delay-based data to have a value of the status data        occurring at the end of the delay,    -   action 204: setting dampening-based data to have the value of        the status data if a penalty value fulfils a condition defined        with one or more penalty thresholds, and otherwise action 205:        setting the dampening-based data to have the off-value, and    -   action 206: setting the report data to have a value of the        delay-based data if the dampening-based data has the on-value,        and otherwise action 207: setting the report data to have the        off-value.

In order to manage the above-mentioned penalty value, the methodcomprises the following actions:

-   -   action 208: setting penalty control data to have a preventive        value in response to a situation in which increasing the penalty        value during a time window exceeds a predetermined limit, the        time-window including the current moment of time and having a        pre-determined temporal length,    -   action 209: increasing the penalty value in response to a        situation in which i) the status data changes from the on-value        to the off-value and ii) the penalty control data has a value        other than the preventive value, and    -   action 210: decreasing the penalty value in accordance with a        predetermined rule over time.

A method according to an exemplifying and non-limiting embodiment of theinvention comprises setting the penalty control data to have thepreventive value if the penalty value has been increased apre-determined number of times during the time-window. Thepre-determined number can be e.g. 1, 2, or 3.

In a method according to an exemplifying and non-limiting embodiment ofthe invention, a change of the status data from the on-value to theoff-value and causing an activation of the delay timer corresponds to abeginning of a new time-window whose temporal length is the temporallength of the delay. The penalty value can be increased at the beginningof the time-window. In this exemplifying case, the increase of thepenalty value carried out at the beginning of the time-window representsat least a part of the amount being added to the penalty value duringthe time-window.

In a method according to an exemplifying and non-limiting embodiment ofthe invention, a change of the status data from the off-value to theon-value and causing an activation of the delay timer corresponds to abeginning of a new time-window whose temporal length is a temporallength of the delay.

In a method according to an exemplifying and non-limiting embodiment ofthe invention, the time-window is a sliding time-window so that thecurrent moment of time is the end-point of the sliding time-window.

In a method according to an exemplifying and non-limiting embodiment ofthe invention, the time-window is a step-wise proceeding time-window sothat the time-window is shifted step-wise forward by the temporal lengthof the time-window when the current moment of time reaches the end-pointof the time-window.

A method according to an exemplifying and non-limiting embodiment of theinvention comprises multiplying the penalty value with a coefficientless than one at successive moments of time so as to decrease thepenalty value.

A method according to an exemplifying and non-limiting embodiment of theinvention comprises setting the dampening-based data to have the valueof the status data if the penalty value is less than a penaltythreshold, and otherwise setting the dampening-based data to have theoff-value.

A method according to an exemplifying and non-limiting embodiment of theinvention comprises setting the dampening-based data to have the valueof the status data if one of the following conditions a) and b) isfulfilled, and otherwise setting the dampening-based data to have theoff-value:

-   -   a) the penalty value is less than a lower penalty threshold, or    -   b) the penalty value is at least the lower penalty threshold and        less than a higher penalty threshold and the penalty value has        not reached the higher penalty threshold after a most recent        time when the penalty value was less than the lower penalty        threshold.

A computer program according to an exemplifying and non-limitingembodiment of the invention comprises computer executable instructionsfor controlling a programmable processor to carry out actions related toa method according to any of the above-described exemplifyingembodiments of the invention.

A computer program according to an exemplifying and non-limitingembodiment of the invention comprises software modules for generatingreport data related to a status of an interface of a network element.The software modules comprise computer executable instructions forcontrolling a programmable processor to:

-   -   receive status data having an on-value when the interface is        utilizable and an off-value when the interface is        non-utilizable,    -   activate a delay timer in response to a situation in which the        status data changes while the delay timer is inactive,    -   set, at an end of a delay determined by the delay timer,        delay-based data to have a value of the status data occurring at        the end of the delay,    -   set dampening-based data to have the value of the status data if        a penalty value fulfils a condition defined with one or more        penalty thresholds, and otherwise set the dampening-based data        to have the off-value, and    -   set the report data to have a value of the delay-based data if        the dampening-based data has the on-value, and otherwise set the        report data to have the off-value.

In order to manage the above-mentioned penalty value, the softwaremodules comprise computer executable instructions for controlling theprogrammable processor to:

-   -   set penalty control data to have a preventive value in response        to a situation in which increasing the penalty value during a        time window exceeds a predetermined limit, the time-window        including the current moment of time and having a pre-determined        temporal length,    -   increase the penalty value in response to a situation in        which i) the status data changes from the on-value to the        off-value and ii) the penalty control data has a value other        than the preventive value, and    -   decrease the penalty value in accordance with a predetermined        rule over time.

The above-mentioned software modules can be e.g. subroutines orfunctions implemented with a suitable programming language and with acompiler suitable for the programming language and the programmableprocessor under consideration. It is worth noting that also a sourcecode corresponding to a suitable programming language represents thecomputer executable software modules because the source code containsthe information needed for controlling the programmable processingsystem to carry out the above-presented modification actions andcompiling changes only the format of the information. Furthermore, it isalso possible that the programmable processing system is provided withan interpreter so that a source code implemented with a suitableprogramming language does not need to be compiled prior to running.

A computer program product according to an exemplifying and non-limitingembodiment of the invention comprises a computer readable medium, e.g. acompact disc “CD”, encoded with a computer program according to anembodiment of invention.

A signal according to an exemplifying and non-limiting embodiment of theinvention is encoded to carry information defining a computer programaccording to an embodiment of invention. In this exemplifying case, thecomputer program can be downloadable from a server that may constitutee.g. a part of a cloud service.

The specific examples provided in the description given above should notbe construed as limiting the scope and/or the applicability of theappended claims. Lists and groups of examples provided in thedescription given above are not exhaustive unless otherwise explicitlystated.

What is claimed is:
 1. A device for generating report data related to astatus of an interface of a network element, the report data beingsuitable for informing a control plane about the status of the interfaceso that flapping between utilizable and non-utilizable states of theinterface is filtered out from the report data, the device comprising adelay timer and a processor system configured to: receive status datahaving an on-value when the interface is utilizable and an off-valuewhen the interface is non-utilizable, initialize, in response to asituation which the status data is received for a first time,delay-based data to have a value of the status data and dampening-baseddata to have the value of the status data, activate the delay timer inresponse to a situation in which the status data changes while the delaytimer is inactive, set, at an end of a delay determined by the delaytimer, the delay-based data to have a value of the status data occurringat the end of the delay, set, regardless of the delay timer, thedampening-based data to have the value of the status data if a penaltyvalue fulfils a condition defined with one or more penalty thresholds,and otherwise set the dampening-based data to have the off-value, set,regardless of the delay timer, the report data to have a value of thedelay-based data if the dampening-based data has the on-value, andotherwise set the report data to have the off-value, decrease,regardless of the delay timer and in response to a situation in whichthe penalty value is greater than zero, the penalty value in accordancewith a predetermined rule over time, set, regardless of the delay timer,penalty control data to have a preventive value in response to asituation in which increasing the penalty value during a time windowexceeds a predetermined limit, the time-window including a currentmoment of time and having a pre-determined temporal length, andincrease, regardless of the delay timer, the penalty value in responseto a situation in which i) the status data changes from the on-value tothe off-value and ii) the penalty control data has a value other thanthe preventive value.
 2. A device according to claim 1, wherein theprocessor system is configured to set the penalty control data to havethe preventive value if an amount exceeding an increase limit has beenadded to the penalty value during the time-window.
 3. A device accordingto claim 1, wherein the processor system is configured to set thepenalty control data to have the preventive value if the penalty valuehas been increased a pre-determined number of times during thetime-window.
 4. A device according to claim 2, wherein the processorsystem is configured to set the penalty control data to have thepreventive value if the penalty value has been increased apre-determined number of times during the time-window.
 5. A deviceaccording to claim 1, wherein a change of the status data from theon-value to the off-value and causing an activation of the delay timercorresponds to a beginning of a new time-window whose temporal length isa temporal length of the delay determined by the delay timer that wasactivated.
 6. A device according to claim 5, wherein the processorsystem is configured to increase the penalty value at the beginning ofthe new time-window, the increase of the penalty value carried out atthe beginning of the new time-window representing at least a part of anamount being added to the penalty value during the new time-window.
 7. Adevice according to claim 1, wherein a change of the status data fromthe off-value to the on-value and causing an activation of the delaytimer corresponds to a beginning of a new time-window whose temporallength is a temporal length of the delay.
 8. A device according to claim1, wherein the processor system is configured to set the time-window tobe a sliding time-window so that the current moment of time is anend-point of the sliding time-window.
 9. A device according to claim 1,wherein the processor system is configured to set the time-window to bea step-wise proceeding time-window so that the time-window is shiftedstep-wise forward by the temporal length of the time-window when thecurrent moment of time reaches an end-point of the time-window.
 10. Adevice according to claim 1, wherein the processor system is configuredto multiply the penalty value with a coefficient less than one atsuccessive moments of time so as to decrease the penalty value.
 11. Adevice according to claim 1, wherein the processor system is configuredto set the dampening-based data to have the value of the status data ifthe penalty value is less than a penalty threshold, and otherwise to setthe dampening-based data to have the off-value.
 12. A device accordingto claim 1, wherein the processor system is configured to set thedampening-based data to have the value of the status data if one of thefollowing conditions a) and b) is fulfilled, and otherwise to set thedampening-based data to have the off-value: a) the penalty value is lessthan a lower penalty threshold, or b) the penalty value is at least thelower penalty threshold and less than a higher penalty threshold and thepenalty value has not reached the higher penalty threshold after a mostrecent time when the penalty value was less than the lower penaltythreshold.
 13. A network element for a data transfer network, thenetwork element comprising: interfaces for connecting to the datatransfer network, a processing system for running a control plane forconfiguring the network element to operate as a part of the datatransfer network and for running a data plane for forwarding data, and adevice for generating report data so as to inform at least the controlplane about a status of at least one of the interfaces of the networkelement, the report data being suitable for informing the control planeabout the status of the at least one of the interfaces so that flappingbetween utilizable and non-utilizable states of the interface isfiltered out from the report data, wherein the device comprises a delaytimer and a processor system configured to: receive status data havingan on-value when the interface is utilizable and an off-value when theinterface is non-utilizable, initialize, in response to a situationwhich the status data is received for a first time, delay-based data tohave a value of the status data and dampening-based data to have thevalue of the status data, activate the delay timer in response to asituation in which the status data changes while the delay timer isinactive, set, at an end of a delay determined by the delay timer, thedelay-based data to have a value of the status data occurring at the endof the delay, set, regardless of the delay timer, the dampening-baseddata to have the value of the status data if a penalty value fulfils acondition defined with one or more penalty thresholds, and otherwise setthe dampening-based data to have the off-value, set, regardless of thedelay timer, the report data to have a value of the delay-based data ifthe dampening-based data has the on-value, and otherwise set the reportdata to have the off-value, decrease, regardless of the delay timer andin response to a situation in which the penalty value is greater thanzero, the penalty value in accordance with a predetermined rule overtime, set, regardless of the delay timer, penalty control data to have apreventive value in response to a situation in which increasing thepenalty value during a time window exceeds a predetermined limit, thetime-window including a current moment of time and having apre-determined temporal length, and increase, regardless of the delaytimer, the penalty value in response to a situation in which i) thestatus data changes from the on-value to the off-value and ii) thepenalty control data has a value other than the preventive value.
 14. Anetwork element according to claim 13, wherein the network element is atleast one of the following: an Internet Protocol IP router, aMultiProtocol Label Switching MPLS switch, a packet optical switch, anEthernet switch, a software-defined networking “SDN” controlled networkelement.
 15. A method for generating report data related to a status ofan interface of a network element, the report data being suitable forinforming a control plane about the status of the interface so thatflapping between utilizable and non-utilizable states of the interfaceis filtered out from the report data, the method comprising: receivingstatus data having an on-value when the interface is utilizable and anoff-value when the interface is non-utilizable, initializing, inresponse to a situation which the status data is received for a firsttime, delay-based data to have a value of the status data anddampening-based data to have the value of the status data, activating adelay timer in response to a situation in which the status data changeswhile the delay timer is inactive, setting, at an end of a delaydetermined by the delay timer, the delay-based data to have a value ofthe status data occurring at the end of the delay, setting, regardlessof the delay timer, the dampening-based data to have the value of thestatus data if a penalty value fulfils a condition defined with one ormore penalty thresholds, and otherwise setting the dampening-based datato have the off-value, setting, regardless of the delay timer, thereport data to have a value of the delay-based data if thedampening-based data has the on-value, and otherwise setting the reportdata to have the off-value, decreasing, regardless of the delay timerand in response to a situation in which the penalty value is greaterthan zero, the penalty value in accordance with a predetermined ruleover time, setting, regardless of the delay timer, penalty control datato have a preventive value in response to a situation in whichincreasing the penalty value during a time window exceeds apredetermined limit, the time-window including a current moment of timeand having a pre-determined temporal length, and increasing, regardlessof the delay timer, the penalty value in response to a situation inwhich i) the status data changes from the on-value to the off-value andii) the penalty control data has a value other than the preventivevalue.
 16. A non-transitory computer readable medium encoded with acomputer program for generating report data related to a status of aninterface of a network element, the report data being suitable forinforming a control plane about the status of the interface so thatflapping between utilizable and non-utilizable states of the interfaceis filtered out from the report data, the computer program comprisingcomputer executable instructions for controlling a programmableprocessor to: receive status data having an on-value when the interfaceis utilizable and an off-value when the interface is non-utilizable,initialize, in response to a situation which the status data is receivedfor a first time, delay-based data to have a value of the status dataand dampening-based data to have the value of the status data, activatea delay timer in response to a situation in which the status datachanges while the delay timer is inactive, set, at an end of a delaydetermined by the delay timer, the delay-based data to have a value ofthe status data occurring at the end of the delay, set, regardless ofthe delay timer, the dampening-based data to have the value of thestatus data if a penalty value fulfils a condition defined with one ormore penalty thresholds, and otherwise set the dampening-based data tohave the off-value, set, regardless of the delay timer, the report datato have a value of the delay-based data if the dampening-based data hasthe on-value, and otherwise set the report data to have the off-value,decrease, regardless of the delay timer and in response to a situationin which the penalty value is greater than zero, the penalty value inaccordance with a predetermined rule over time, set, regardless of thedelay timer, penalty control data to have a preventive value in responseto a situation in which increasing the penalty value during a timewindow exceeds a predetermined limit, the time-window including acurrent moment of time and having a pre-determined temporal length, andincrease, regardless of the delay timer, the penalty value in responseto a situation in which i) the status data changes from the on-value tothe off-value and ii) the penalty control data has a value other thanthe preventive value.